For weapons systems to be effective, the location of a target must be known in a coordinate system, such as longitude, latitude and elevation. These coordinates must be extremely accurate in order to properly guide a weapon and to avoid collateral damage.
In the past attempts have been made to improve the determination of coordinates. Often this includes teams of observers equipped with various and cumbersome portable systems to either determine target position coordinates or to designate the target by laser illumination in the case of laser homing systems. Despite these advances teams are still equipped with maps and are required to perform calculations in the field.
In addition, determining a true bearing to a target or a location is a concern due to the difference between magnetic readings of raw and true directions. The difference between true north and magnetic north at a location is called magnetic declination. Correction of magnetic declination is extremely important as the difference in degrees on a 0–360 degree scale between the bearing to the magnetic north pole and the bearing to the geographic north pole, or true North Pole in many areas of the earth may amount up to about 30 degrees and above. Due to declination, maps are printed marked with the local values of declination.
Known instruments for aiding in the use of maps, are very limited in their usefulness, particularly for military purposes. One such limitation is that they are applicable to a single scale map because each instrument is calibrated for use with one of several military scaled maps, as for example 1:25,000, 1:50,000 or 1:125,000. Another limitation of known instruments, particularly for military uses, is that the user has a need in the effective use of a map to make arithmatical computations and, therefore, military recruits must undergo extensive training in map reading. Some of the arithmatical computations involve converting magnetic azimuths to grid azimuths and conversion to back azimuths when it is desired to locate on the map an unknown point from two known points, which functions are referred to as “resection” and “intersection.” Also, in determining the total distance along a sinuous path, e.g. a road or railroad track, the user must add the straight portions of the path between the curved portions. A further limitation of known map reading devices is that the artillery uses instruments in which angular directions are measured in mils rather than degrees for more accurate aiming of the weapons. Thus, artillery personnel and those spotting for artillery units must have special map reading and plotting instruments. Obviously, where in the use of heretofore known map reading instruments computations are required, the need for paper and/or a writing implement poses a problem, particularly under actual field conditions where paper and a writing tool is not, always available to the map user. Also, map reading and plotting instruments of heretofore known types require the user to draw lines on a map and, in absence of available paper, the user may use the map for making computations. These writings on a map lead to short map life and leaves marks which, even if erased, are visible or can be made visible and may give aid to an enemy if the map is captured.
Determining target coordinates in the field is cumbersome and prone to error using the methods described. Accordingly, there is a need for rapidly calculated, accurate true coordinates, generated without maps and hand calculations, which may be used for various applications including but not limited to directing weapons to a target.